The invention relates to a method for producing or repairing cooling channels in monocrystalline components of gas turbines.
Gas turbine components impacted by hot gas have been provided with cooling air structures for a long time in order to be able to, on the one hand, increase the temperature of the hot gas and, on the other hand, extend the life span of the affected parts. Usually, these gas turbine components are cast and consist of monocrystalline super alloys. Such a super alloy based on Ni is disclosed, for example, in U.S. Pat. No. 5,759,301. This alloy has proven itself especially for very thin walls as they occur in components of gas turbines, since it does not have any grain boundaries. Grain boundaries would have a negative effect on material properties. The cooling channels can be produced during casting; a known technology for this is the Castcool technology of Allison company (cf. Burkholder et al., Allison engine testing CMSX-4 single crystal turbine blades and vanes, 3rd International Charles Parsons Turbine Conference, ISSN 0-901716-89-8). This Castcool casting process works with a ceramic core that is integrated into the casting form. But this process is unfortunately relatively expensive, due to the relatively high waste rate in the production of the very thin walls of the cooling channels. In particular, there is no way to repair chipped components with this process.
In addition, other processes are known for producing the cooling channels, among them the LIGA process (cf. xe2x80x9cThe Miniaturization Technologies-Past, Present and Futurexe2x80x9d, Frazier et al., from IEEE Transactions on industrial electronics, 1995, V42, n5 (Oct.), p. 423-430, ISSN 0278-0046), and laser-based processes, such as LENS technology (Laser Engineered Net Shaping). But in practice, they are not used for producing cooling channels in monocrystalline structures, since during the production, especially as a result of the temperature action, amorphous and multicrystalline structures are created, which destroy the favorable properties of the monocrystalline structures in relation to firmness and ductility, and the very thin walls of gas turbines are more susceptible to the stresses they are exposed to. In order to avoid these disadvantages, a monocrystalline structure without grain boundaries is needed.
A process for producing a cooling structure of an airfoil is known from U.S. Pat. No. 5,640,767. But this process has the disadvantage that the base material and the second layer applied consist of different materials. This results in a weakening of the component at the contact point between the two layers.
European patent application No. EP 892 090 A1 in contrast describes a process for producing monocrystalline structures. This process employs an energy beam with a high energy density, for example a laser beam, an electron beam, or a light arc that melts a base material. To this melted area is added material that is identical to the base material or has a similar crystal structure as the base material and is also melted. During this process, the addition of energy is regulated and controlled in such a way that the solidification speed and temperature gradient result in a directional, dendritically crystalline, and not in a globulitic, solidification.
A process for repairing a monocrystalline structure is also known from European patent application No. EP 740 976 A1.
It is the objective of this invention to create a process that facilitates the production or repair of cooling channels of a gas turbine component consisting of monocrystalline structures.
According to the invention, this objective is achieved in a process in which the monocrystalline gas turbine component is cast, thermally stable filling material is applied, a monocrystalline layer is epitactically created over the thermally stable filling material, and the thermally stable filling material is removed.
The invented process has the advantage that it facilitates the production of gas turbine components with cooling channels. The thermally stable filling material can be easily removed, for example, by etching. The rate of waste of the process and its associated costs are favorably low when compared with the state of the art Castcool technology. The process also can be used several times consecutively in order to produce superimposed cooling channels. This process also makes it possible to repair cooling channel of a chipped gas turbine component.